1. Field of the Invention
The present invention relates to a fuel gas heating control equipment of a gas turbine, and especially, relates to fuel gas heating control equipment which controls the flow rate of a fuel gas passing through a heater being installed to a fuel gas system. In addition, the present invention relates to a gas turbine power generation facility being provided with the fuel gas heating control equipment as aforementioned.
2. Description of the Prior Art
A conventional gas turbine has a heater installed to a stage preceding a combustor in order to enhance combustion efficiency of a fuel. (See the Japanese Patent Application Laid-Open No. H11-236824.)
FIG. 10 is a diagram showing an example of a fuel system of a conventional general gas turbine power generation facility. In a gas turbine power generation facility 1, a compressor 2, a gas turbine 3 and a generator 5 are connected concentrically, and the generator 5 generates electric power by having the gas turbine 3 provided with torque for rotation by a combustion gas being supplied from the combustor 4
The gas turbine power generation facility 1 provides the combustor 4 with high pressure air being generated by the compressor 2 and at the same time causes combustion by supplying a fuel gas to the combustor 4 from a combustor flow control valve 8. In addition, by supplying the high pressure air being generated by the compressor 2 to a heater 6 and heating a specific amount of the fuel gas being supplied to the heater 6 in the stage preceding the combustor 4, combustion efficiency of the combustor 4 is enhanced. A bypass flow control valve 9 is for a purpose of adjusting the flow rate of a fuel gas being supplied to the heater 6, and a part of the fuel gas being supplied to the bypass flow control valve 9 is supplied to a subsequent stage to the combustor 4 without being heated by bypassing the heater 6. In the subsequent stage to the heater 6, the fuel gas being heated in the heater 6 and the fuel gas not being heated by bypassing the heater 6 are mixed and supplied to the combustor flow control valve 8. Additionally, the subsequent stage to the heater 6 is provided with a temperature-detecting element 7 for measuring the gas temperature of the fuel gases being mixed.
Moreover, the gas turbine power generation facility 1 is provided with a combustor flow control portion 11 specifying the lift of a combustion flow control valve 8 and a bypass flow control portion 12 controlling a control input of the bypass flow control valve 9. By supplying the combustor flow control valve 8 with a value being specified by the combustor flow control portion 11 as the control input, the lift of the combustor flow control valve 8 is adjusted, thereby adjusting the flow rate of the fuel gas to be supplied to the combustor 5. In addition, by having the bypass flow control portion 12 adjust the control input of the bypass flow control valve 9 based on a predetermined calculation, the flow rate of the fuel gas bypassing the heater 6 is adjusted.
The bypass flow control portion 12 is provided with a specified-temperature-determining portion 13 which determines and outputs an aimed specified temperature being uniquely determined in accordance with the output at the time when the output of the generator 5 is supplied; a subtracter 15 which calculates a difference value by comparing with an aimed specified temperature being determined by the specified-temperature-determining portion 13 when the fuel gas temperature is supplied by the temperature-detecting element 7 being provided to the subsequent stage to the heater 6; and a PI calculation portion 14 which performs calculations for PI control for the subtraction results of the subtracter 15 and obtains a control input of the bypass flow control valve 9. The PI calculation portion 14 is provided in advance with a gain “K” and a time constant “T” that are necessary values for calculations for PI control and performs calculations on the basis of the gain “K” and the time constant “T.” Then, the control input being calculated by the PI calculation portion 14 is supplied to the bypass flow control valve 9, and the lift of the bypass flow control valve 9 is adjusted on the basis of the control input.
When the output of the generator 5 is supplied, the specified-temperature-determining portion 13 provides the PI calculation portion 14 with a value as a specified temperature, which is uniquely determined in accordance with the output at the time. FIG. 11 is an example of a graph showing the relation between the generator output and the specified temperature.
As shown in FIG. 11, the specified-temperature-determining portion 13 specifies the aimed specified temperature in a manner that the aimed specified temperature ascends in accordance with an increase in the generator output until the generator output reaches the maximum output Wx. In addition, when the generator output is more than the maximum output Wx, the aimed specified temperature is set to be a predetermined value “τx.”
In accordance with a method disclosed in the Japanese Patent Application Laid Open No. H11-23682, as shown in FIG. 11, the aimed specified temperature being specified by the specified-temperature-determining portion 13 increases rapidly, in accordance with an increase in the generator output during load-up (including start-up). Therefore, it is necessary for the bypass flow control portion 12 to respond to the rapid change by setting the value of the time constant “T” in the PI control to be small.
However, when the time constant “T” is made small, even a slight change is responded to although the generator output has attained the aimed maximum output Wx. As a result, there exists a problem that the combustion gas temperature cannot be stable but fluctuate, which causes the combustion state in a combustor to be unstable.
On the contrary, when the time constant “T” is increased, there exists a problem that an accurate control is impossible because the fuel gas temperature cannot follow a rapid change in the aimed specified temperature in a condition where the generator output fluctuates during load-up and the like.